Former world No. 1 Luke Donald was assessed a two-stroke penalty in the first round of the Masters on Thursday.

The penalty occurred after Donald played his third shot from a greenside bunker on the par-4 ninth hole. Donald left his third shot in the bunker and violated Rule 13-4 by grounding his club in a hazard (the bunker) before playing his fourth shot.

According to a Yahoo! Sports story, the infraction was brought to the attention of officials by a patron who witnessed the incident.

The report also states:

According to Augusta National spokesman Steve Ethun, Donald was informed of the penalty after his round but prior to signing his scorecard. (Had he signed an incorrect scorecard, Donald would have been disqualified.) Donald took a first-round score of 79 (+7), a total that included the two-stroke penalty. Donald made a quadruple-bogey 8 on the hole and eventually signed for a 7-over 79.

Except as provided in the Rules, before making a stroke at a ball that is in a hazard (whether a bunker or a water hazard) or that, having been lifted from a hazard, may be dropped or placed in the hazard, the player must not:

a. Test the condition of the hazard or any similar hazard;

b. Touch the ground in the hazard or water in the water hazard with his hand or a club; or

c. Touch or move a loose impediment lying in or touching the hazard.

After the round, Donald took to Twitter to explain the incident:

Got a 2 shot penalty on the 9th today. Left my bunker shot in the bunker and touched the sand before my next shot. Pretty dumb mistake